Mild experimental brain injury differentially alters the expression of neurotrophin and neurotrophin receptor mRNAs in the hippocampus

The molecular events responsible for impairments in cognition following mil d traumatic brain injury are poorly understood. Neurotrophins, such as brai n-derived neurotrophic factor (BDNF), have been identified as having a role in learning and memory. We have previously demonstrated that following exp erimental brain trauma of moderate severity (2.0-2.1 atm), mRNA levels of B DNF and its high-affinity receptor, trkB, are increased bilaterally in the hippocampus for several hours, whereas NT-3 mRNA expression is decreased. I n the present study, we used in situ hybridization to compare BDNF, trkB, N T-3, and trkC mRNA expression in rat hippocampus at 3 or 6 h after a latera l fluid percussion brain injury (FPI) of mild severity (1.0 atm) to sham-in jured controls at equivalent time points. Mild FPI induced significant incr eases in hybridization levels for BDNF and trkB mRNAs, and a decrease in NT -3 mRNA in the hippocampus. However, in contrast to the bilateral effects o f moderate experimental brain injury, the present changes with mild injury were restricted to the injured side. These findings demonstrate that even a mild traumatic brain injury differentially alters neurotrophin and neurotr ophin receptor levels in the hippocampus. Such alterations may have importa nt implications for neural plasticity and recovery of function in people wh o sustain a mild head injury. (C) 1999 Academic Press.